The present invention relates generally to a coating for a substrate. More specifically, the present invention relates to an ink jet printable coating and coating system for holographic paper.
Holographic paper, i.e., paper having a three dimensional variable image, and diffraction paper, i.e., paper having a two dimensional variable image, are widely available on the market today. The holographic and/or diffraction (holographic) paper is known as an optically variable device, i.e., the image appearance varies depending on the light source, light angle and the viewing angle. The imagery itself is reproduced on the surface of the paper, or other substrate, from an original holographic master by micro-embossing into a coating on the surface of the paper. The surface is then vacuum metallized to provide a very bright, shiny, metallic finish that brings out the holographic imagery and makes it visible. Holographic paper is printed upon commercially using special inks that dry by oxidation and/or ultra violet curing. Additionally, some commercial operations use inks that dry by removal of solvents or water.
Ink jet printing on decorative paper has a great deal of appeal in the desk top computer publishing market, because it is interactive and has an eye-catching appearance. Greeting cards, presentation folders, business cards, labels, tags, placards, stationery, artworks, etc., are digitally printed in the office and at home on ink jet printers in wide spread use today. Ink jet printing uses water based or solvent based ink jet inks.
Problematically, holographic paper is not readily compatible with water based ink jet inks. That is, because the surface of the holographic paper is not absorptive and is nearly inert, it is difficult for the water based ink jet inks to adhere or penetrate the surface.
Solvent based ink jet inks are more readily compatible with holographic paper. However, the solvents, e.g., ethyl acetate, methyl keytone and acetone, that comprise the solvent based inks are hazardous to the environment and often require special handling. Therefore water based ink jet inks, which are not as compatible with holographic papers, are much more widely used in the desk top computer publishing market.
There is a need, therefore, for an improved method and apparatus for ink jet printing on holographic paper.
This invention offers advantages and alternatives over the prior art by providing an ink jet printable coating for holographic paper. The coating utilizes a primer layer, preferably having a surface tension in the range of 35-80 dynes, and a secondary layer. The secondary layer includes a plurality of microscopic pores which are preferably 1 to 6 microns in diameter. The pores are sized to allow ink jet ink to penetrate during the printing process. Advantageously, the coating is compatible to both water based and solvent based inks. The pores serve to provide a site to which the ink jet ink can anchor and set, thus preventing the ink from running when initially applied to the surface. Furthermore, the pores actually create more surface area for the water to be absorbed into. Additionally, the secondary layer is porous enough to absorb the ink as it dries. The deeper the secondary layer, the further the ink can penetrate for greater adhesion to the surface.
In an exemplary embodiment of the invention, a coating is disposed on an optically variable device, e.g., holographic paper, which has an image with a variable appearance through the coating. The coating comprises a primer layer which includes a member selected from the group consisting of acrylic resins, polyester resins, urethane resins, vinyl resins and nitrocellulose. The primer layer is disposed on the surface of the optically variable device. The coating also comprises at least one secondary layer which includes a member selected from the group consisting of polyvinyl alcohol, gelatin, cellulose, acrylic resins and polyvinyl propylene. The secondary layer is disposed on the primer layer. The secondary layer has a plurality of microscopic pores disposed therein for receiving ink jet ink.
In an alternative exemplary embodiment of the invention, a method of coating an optically variable device having an image with a variable appearance through the coating is presented. The method comprises first coating the optically variable device with a primer layer including a member selected from the group consisting of acrylic resins, polyester resins, urethane resins, vinyl resins and nitrocellulose. Next, the method comprises coating at least one secondary layer including a member selected from the group consisting of polyvinyl alcohol, gelatin, cellulose, acrylic resins and polyvinyl propylene on the primer layer, via the coating process known as rotogravure. Thus, the method forms a plurality of microscopic pores on the secondary layer for receiving ink jet ink.